23 Obnoxious weeds to watch out in your farm or garden1

1. Pigweed - Amaranthus spp

You might find two common types of pigweeds; low amaranth (deflexus) and tall amaranth (palmeri).

Palmer pigweed is a broadleaf species of edible flowering plant in the amaranth genus.

This wild edible can be a beneficial weed as well as a companion plant serving as a trap for leaf miners and some other pests; also, it tends to shelter ground beetles (which prey upon insect pests)

The plant can be toxic to livestock animals due to the presence of nitrates in the leaves.

Palmer amaranth has a tendency to absorb excess soil nitrogen, and if grown in overly fertilized soils, it can contain excessive levels of nitrates, even for humans.

Like spinach and many other leafy greens, amaranth leaves also contain oxalic acid, which can be harmful to individuals with kidney problems if consumed in excess.

Palmer amaranth may be the most aggressive pigweed species with respect to growth rate and competitive ability

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2. Crabgrass – Digitaria spp

Digitaria is a genus of plants in the grass family native to tropical and warm temperate regions.

Crabgrass is considered lawn pest by most gardeners.

While it’s true some species are weeds, some are used as food in Africa. Their seeds are ground and the flour used to make porridge.

Both the hairy crabgrass and smooth crabgrass are specifically problematic weeds in lawns and gardens, growing especially well in thin lawns that are watered lightly, under-fertilized, and poorly drained.

One plant is capable of producing 150,000 seeds per season which makes them difficult to control.

When the plants die, they leave large voids in the lawn. The voids then become prime areas for the crabgrass seeds to germinate

Biological control is preferable over herbicide use on lawns, as crabgrass emergence is not the cause of poor lawn health but a symptom, and it will return annually if the lawn is not restored with fertilization and proper watering.

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3. Dandelion - Taraxacum officinale

Taraxacum is a large genus of flowering plants in the family Asteraceae which consists of species commonly known as dandelion.

The flower heads are yellow to orange coloured, and are open in the daytime, but closed at night. Stems and leaves exude a white, milky latex when broken.

Many similar plants in the Asteraceae family with yellow flowers are sometimes known as false dandelions.

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4. Oxalis – Oxalis spp

Oxalis is a large genus of flowering plants in the wood-sorrel family Oxalidaceae. Many of the species are known as wood sorrels

All Oxalis weeds are considered highly aggressive, and should be eliminated completely from your lawns and gardens in order to be controlled.

An infestation can occur in almost any environment.

Some species for instant Bermuda-buttercup and creeping wood sorrel– are pernicious, invasive weeds when escaping from cultivation outside their native ranges; the ability of most wood-sorrels to store reserve energy in their tubers makes them quite resistant to most weed control techniques.

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5. Purslane - Portulaca oleracea

Purslane has a taproot with fibrous secondary roots and is able to tolerate poor compacted soils and drought.

Although purslane is considered a weed in most parts of the world, it may be eaten as a leaf vegetable.

In addition, you can use the purslane as a companion plant since it serves as a ground cover that create humid microclimate for nearby plants, stabilising ground moisture.

Its deep roots bring up moisture and nutrients that those plants can use, and some, including corn, will follow purslane roots down through harder soil that they cannot penetrate on their own (ecological facilitation).

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Clover – Trifolium spp

Clover or trefoil are common names for plants of the genus Trifolium. They are small annual, biennial, or short-lived perennial herbaceous plants. Clover can be evergreen.

Several species of clover are extensively cultivated as fodder plants.

The clover is palatable to and nutritious for livestock; it fixes nitrogen, reducing the need for synthetic fertilizers; it grows in a great range of soils and climates; and it is appropriate for either pasturage or green composting.

The seeds can survive high heat, low temperatures and can stay dormant for years before germinating.

6. Thistles - Onopordum acanthium

Thistle is a flowering plant in the family Asteraceae. It is a vigorous biennial plant with coarse, spiny leaves and conspicuous spiny-winged stems.

It is a biennial plant, producing a large rosette of spiny leaves the first year.

Thistle forms a stout, fleshy taproot that may extend down 30 cm or more for a food reserve.

For the same reason, the thistle is now considered a major agricultural and wildland noxious weed.

It has been recorded from nearly 50 countries.

It is difficult to eradicate because of its drought resistance. It can spread rapidly and eventually dense stands prohibit foraging by livestock.

The weed adapts best to areas along rivers and streams, but can be a serious problem in pastures, grain fields and range areas.

A single plant is imposing enough, but an entire colony can ruin a pasture or destroy a park or campsite, sometimes forming tall, dense, impenetrable stands.

Besides creating an impenetrable barrier to humans and animals, the plant nearly eliminates forage use by livestock and some mammal species such as deer and elk

Small infestations may be physically removed or cut a few centimetres below the soil surface ensuring that no leaves remain attached to prevent regrowth.

Because of their shorter life cycle, cotton thistle plants can be effectively treated with herbicides. All herbicide treatments should be applied at the rosette stage of the plant.

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7. Lamb’s Quarters - Chenopodium album

Chenopodium album is a fast-growing weedy annual plant in the genus Chenopodium. Though cultivated in some regions, the plant is elsewhere considered a weed.

It is one of the more robust and competitive weeds, capable of producing crop losses of up to 13% in corn, 25% in soybeans, and 48% in sugar beets at an average plant distribution.

It may be controlled by dark tillage, rotary hoeing, or flaming when the plants are small. Crop rotation of small grains will suppress an infestation.

It is easily controlled with a number of pre-emergence herbicides.

Chenopodium album is vulnerable to leaf miners, making it a useful trap crop as a companion plant. Growing near other plants, it attracts leaf miners which might otherwise have attacked the crop to be protected.

It is a host plant for the beet leafhopper, an insect which transmits curly top virus to beet crops.

As some of the common names suggest, it is also used as a feed (both the leaves and the seeds) for chickens and other poultry.

8. Quackgrass – Agropyron repens

Quackgrass is a perennial and a troublesome weed to eliminate from the home landscape. The Latin name means a 'sudden field of fire', and attests to its ability to take over lawns, fields and gardens.

Quackgrass, also commonly known as couch grass, twitch grass, quick grass, scutch grass, and devil's grass, is a widespread and serious weed in Canada.

Traditionally one of the most difficult weeds to control, it remains a problem due to characteristics that enable it to survive and multiply: rapid establishment, an extensive mat of underground rhizomes with the ability to produce new plants, and the ease with which new quackgrass biotypes can be generated through sexual reproduction.

Due to its highly competitive nature, quackgrass can effectively reduce crop yields by as much as 25% to 85% in corn, 19% to 55% in soybeans, and up to 57% in wheat.1

These yield reductions may result from quackgrass' luxurious use of nutrients.

It is estimated that quackgrass can absorb approximately 55%, 45%, and 68% of the total nitrogen, phosphorus and potassium, respectively, available for plant use.

Although quackgrass can cause extensive crop losses, it does have some redeeming qualities. For example, it’s used for pasture or hay.

9. Chickweed - Stellaria media

It is used as a cooling herbal remedy, and grown as a vegetable crop and ground cover for both human consumption and poultry.

Common in lawns and landscaped areas. It inhabits agricultural land and other disturbed sites. It can harbour several viruses and other pests that affect a variety of vegetable crops. Many species of wildlife feed on its leaves and seeds.

Chickweed is a common problem in the lawn and garden and sometimes difficult to control.

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10. Shepherds purse - Capsella bursa-pastoris

Capsella bursa-pastoris, known by its common name shepherd's purse because of its triangular flat fruits which are purse-like, is a small (up to 0.5 m) annual and ruderal flowering plant in the mustard family Brassicaceae.

It is native to Eastern Europe and Asia Minor but is naturalized and considered a common weed in many parts of the world,

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11. Morning glory - Ipomoea purpurea

Morning glory is the common name for over 1,000 species of flowering plants in the family Convolvulaceae, whose current taxonomy and systematics are in flux.

Morning glory weeds in the garden can be viewed as a nemesis due to the rapid spread and ability to take over garden areas.

This hummingbird-attracting plant is an aggressive grower that can quickly strangle desirable plants. Controlling this innocent-looking vine takes determination, time and multiple control methods.

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12. Buckhorn Plantain - Plantago lanceolata

Plantago lanceolata is a species of flowering plant in the plantain family Plantaginaceae.

It is a frequent colonizer of temperate riparian ecosystems, roadsides and waste places. It forms thick, dense colonies that completely crowd out any other herbaceous species.

The success of the species has been partially attributed to its tolerance of a very wide range of soil types, pH and salinity.

Its rhizomes can survive temperatures of −35 °C (−31 °F) and can extend 7 meters (23 ft.) horizontally and 3 meters (9.8 ft.) deep, making removal by excavation extremely difficult. The plant is also resilient to cutting, vigorously resprouting from the roots.

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15. Creeping Charlie

Creeping charlie (Glechoma hederacea) is often called ground ivy due to its appearance and growth habits. Creeping charlie weed is a green vine whose leaves are round with scalloped edges.

The vines have nodes at each of the places where leaves grow and these nodes will form roots if they come in contact with the soil.

This is part of the reason that creeping charlie weed is so frustrating, as you cannot simply pull it up.

While creeping Charlie is considered a broadleaved weed, it cannot be eliminated by broadleaved spectrum herbicides.

Other weeds

16. Nutsedge

Also called nutgrass, is a perennial weed that is often found in turf, and it can be very difficult to get rid of it.

17. Velvetleaf

Is a summer annual broadleaf plant and a problematic weed for many crops in the world, particularly where cotton, corn, or soybeans are major crops.

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18. Quickweed - Galinsoga quadriradiata

Scientifically known as Galinsoga quadriradiata is a species of flowering plant in the daisy family which is known by several common names, including shaggy soldier, Peruvian daisy, hairy galinsoga, and fringed quickweed.

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19. Smartweed

martweed is a common wildflower often found growing along roadsides and railroad tracks. A real nightmare to shade crops.

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20. Poison Ivy

21. Fleabane

22. Nettle

23. Ragweed

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Conclusion

To be able to successful control weeds in your lawn, garden, or pastures; you must first of all understand them beyond common knowledge.

This article that you’ve just read is a starting point to discovering which weeds are friendly and which are foe.

Some of them the benefits outweigh the undesirable and therefore, we can afford to live with them in our gardens.

Good article but I prefer to tolerate some clover in the lawn, rather than use weed and feed products that have been linked to feline leukemia. If it is bad for cats, it can’t be good for children either.

A very common weed (certainly in the western states) that belongs on this list would be “cheeseweed”, Malva parvifolia, and also Malva neglecta. A more “dangerous” weed that also didn’t make the list would be Castorbean plant, Ricinus communis…exceptionally allergenic & very poisonous…invasive and common in the West & in southern states.

Very good article,Chris: The MAIN comment I have to add to your expertise here, IS, that some of these, ARE very relevant edible species and some, AS Amaranthus are food and have been for centuries. Taraxacum leaves are edible and a formidable reservoir of vitamins and minerals. ITS root IS to be dried and then considered valuable for natural antibiotic. Plantago Major, which is the one you show instead of Lanceolata, has medicinal virtues not to be seen with disdain and Purslane, a wondrous Omega 3 reservoir.
So, as to contribute with the other aspects of these WEEDS, is the intention of this comment and of course, appreciate your detailed info, Chris, do keep up the quality job.
Best regards:
Edgar

We should add Goathead Thistle to this list. It is spreading over the western United States. The mature thistle flower heads have terrible spikes that can puncture bicycle tires and inflict painful wounds in humans and pets. The seeds are easily spread and I’ve personally seen the thistles along roads and trails.

Clovers, in pasture, are most often desirable as they fix nitrogen and provide both high quality & digestibility foratge to both horses & ruminants. Cautions include some varieties which lead to more bloat than others & low percent cover (max 10-15%) for horses as they do not need high levels of protein provided.
True dandelion, which you have pictured, is not problematic for grazing animals. It is both palatable and safe. It is also placed in green salads which people eat. While it is a ‘pest’ to some due to aesthetics, focusing on its control, rather than bolstering the desired species is not advisable.
The purpose of the plant community, lawn vs. pasture vs. native meadow conservation, should be a starting point and would help sort out the concerns already expressed by readers of this post.
As for making lists, all States have their Noxious Weeds Lists and have programs in place to deal with the issues of weeds, both terrestrial & aquatic. Many counties also write priority lists and cooperate with private & public land managers to control weeds by contributing know-how, funds and collective action, treatment & monitoring. I encourage you to team up with those folks for greatest impact across land ownership boundaries.

There is never too much biodiversity and many of your weeds are edible. Because nettles (Urtica) do not grow in my neighbourhood, I took the effort to cultivate them, they make a palatable and nutritious vegetable : I use them for soup but a friend has a technique to add them raw to salads. Dandelion (Taraxacum), when it is small in winter, is sold at high prices on the market in Lyon (France). Portulaca oleracea, Capsella bursa-pastoris (before it grows flowers), Stellaria, are also good salads. Plantago major (the one which you show on your picture) in my garden is tastier than lanceolata but this may vary, I do not eat plantain myself. I use occasionally Amaranthus.
Clover seeds are sold in shops in my country, just try to find out what Masanobu Fukuoka did with clover.
You may know the quote of Ralph Waldo Emerson : ‘What is a weed? A plant whose virtues have not yet been discovered.